Compressor protection module and system and method incorporating same

ABSTRACT

An apparatus for monitoring a compressor includes a plurality of sensor inputs for receiving input regarding operating parameters of a compressor, at least one control action output for sending a control action to the compressor; and a control member communicated with the plurality of sensor inputs and the control action output, the control member being adapted to analyze input from the plurality of sensor inputs, to determine a control action based upon the input and to send the control action to the at least one control action output.

BACKGROUND OF THE INVENTION

[0001] The invention relates to a compressor protection and controlmodule and a system and method incorporating same.

[0002] Compressor maintenance and reliability are critical issues. Inconnection with reliability, a malfunctioning compressor can causedifficulties spanning from minor inconvenience to loss of valuablerefrigerated product. Furthermore, compressors themselves are costlyequipment and improper maintenance or operation can result in damagerequiring expensive maintenance or replacement.

[0003] Systems and methods are known for limited, local control andprotection of compressors. Such systems tend to focus on singleparameters to provide for emergency action. Although this is helpful,such systems do not assist in identifying a potential problem before thecompressor is incapacitated.

[0004] In light of the foregoing, it is clear that the need remains forimproved compressor monitoring so as to avoid compressor shut downs, ifpossible, and minimize expense due to compressor repair/replacement,spoilage and the like.

[0005] Therefore, the primary objectives of the present invention are to(1) provide a module for protecting a compressor which detects troublewith the compressor before compressor failure, (2) provide a module thatcan control key operating and control functions based on monitoredoperating conditions and (3) provide such a module, and a system andmethod incorporating same, wherein preventive maintenance isfacilitated.

[0006] Other objects and advantages of the present invention will appearhereinbelow.

SUMMARY OF THE INVENTION

[0007] In accordance with the present invention, the foregoing objectsand advantages have been readily attained.

[0008] According to the invention, an apparatus for monitoring acompressor is provided, which comprises a plurality of sensor inputs forreceiving input regarding operating parameters of a compressor; at leastone control action output for sending a control action to saidcompressor; and a control member communicated with said plurality ofsensor inputs and said control action output, said control member beingadapted to analyze input from said plurality of sensor inputs todetermine a control action based upon said input, and to send saidcontrol action to said at least one control action output.

[0009] A display may be provided and adapted to show sensor inputvalues, control output and alarm status.

[0010] In further accordance with the present invention, a method isprovided for monitoring a compressor, which method comprises the stepsof obtaining input regarding a plurality of compressor operatingparameters; feeding said input to a control member; analyzing said inputwith said control member to determine a control action based upon saidinput; and carrying out said control action on said compressor. Ahistory of such control actions and sensor inputs may be stored forlater retrieval and analysis.

[0011] Still further according to the invention, a compressor andcontrol module system are provided, which comprises a control modulecomprising a plurality of sensor inputs; at least one control actionoutput; and a control member communicated with said plurality of sensorinputs and said control action output, said control member being adaptedto analyze input from said plurality of sensor inputs, to determine acontrol action based upon said input and to said control action to saidat least one control action output.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] A detailed description of preferred embodiments of the presentinvention follows, with reference to the attached drawing, wherein FIG.1 schematically illustrates a functional block diagram of a compressorand module in accordance with the present invention.

DETAILED DESCRIPTION

[0013] In accordance with the present invention, a compressor protectionmodule is provided which advantageously monitors a combination ofcompressor operating parameters and which is programmed to determineappropriate control actions based upon combinations of sensor input.Verification of the control function can also be accomplished bycomparing the actual result to the expected result. The module of thepresent invention can thereby advantageously detect certain failureconditions before failure is imminent, thereby reducing maintenance andrepair costs and avoiding potential damage to refrigerated product. Themodule can also be programmed to maintain application specific operatingparameters as certain operating parameters and alarm setpoints can beadjusted within a limited range.

[0014] Turning now to FIG. 1, a functional block diagram schematicallyillustrates a compressor and module in accordance with the presentinvention.

[0015]FIG. 1 shows a compressor chassis 10 and a module 12 in accordancewith the present invention. Module 12 includes a processor 14 and aplurality of sensor inputs for measuring compressor operatingparameters. These inputs are preferably connected to various probes andtransducers including a discharge thermistor probe 16 for measuringcompressor discharge temperature, a return gas thermistor probe 18 formeasuring return gas temperature or suction temperature, a suctionpressure transducer 20 for measuring suction pressure, a dischargepressure transducer 22 for measuring discharge pressure and an oildischarge pressure transducer 24 for measuring oil discharge pressure.

[0016] As shown in FIG. 1, the sensor inputs may also advantageouslyinclude inputs 26 for power supply, compressor on/off signal and safetyinput signal, a crank case heater current transformer 28 which ispreferably adapted to control and/or detect operation of the crank caseheater of the compressor, an output 30 for liquid injection valvecontrol and outputs 32, 34 for providing unloader control. Inputs formotor current and supply voltage could also be provided.

[0017] Processor 14 in accordance with the invention is advantageouslycommunicated with each of these sensor inputs and has memory programmedwith a series of commands adapted to evaluate different combinations ofinputs from each sensor and thereby identify correct operatingconditions, operating conditions indicating that the compressor is beingimproperly operated, operating conditions indicating that the compressorneeds maintenance, operating conditions that indicate that thecompressor must be operated under different conditions to avoid damage,and the like.

[0018] For example, control unit or processor 14 can advantageously beprogrammed so as to detect conditions such as a flooded start, liquidslugging, inadequate control of liquid injection volumes and liquidfloodback. Each of these conditions can be inferred from differentcombinations of input from the sensor inputs, which will then allow forappropriate control actions to be taken.

[0019] Module 12 of the present invention can also advantageously beprogrammed to maintain a given operating condition and will control thecompressor in order to maintain the programmed operating parameters. Forexample in refrigeration applications the compressor is typicallycontrolled to maintain the suction pressure within a given range. Bymonitoring the suction pressure, module 12 can be programmed to startand stop the compressor and operate the unloaders such that the desiredsuction pressure is maintained.

[0020] The various control actions that may be desirable, along withappropriate input value combinations for using such control actions, arestored in memory in module 12 for use in evaluating actual input andselecting a suitable control action for the compressor.

[0021] In further accordance with the present invention, module 12advantageously is provided having an interface port 36 adapted forconnection with communication capability, for example through CCN/LON orother communication network. This advantageously allows for remoteaccess from and to module 12 so that information can be obtained frommodule 12 by personnel located at a remote location, and information canbe automatically sent by module 12 to a remote location, as dictated bycontrol actions corresponding to combinations of input from the sensorinputs. The communications can also be used to send commands to themodule such as on/off control, unloading control and the modification ofadjustable operating parameters. This communication can be by dedicatedor shared telephone access, for example using a modem, or wirelessaccess, or through any other manner known to persons of ordinary skillin the art.

[0022] Module 12 in accordance with the present invention furtherpreferably includes a human interface 38 which may advantageously be adisplay member for indicating various information to a user, such ascurrent operating status, detected fault conditions, and the like. Thedisplay can also be utilized to modify adjustable operating parameterssuch as unloading and liquid injection setpoints and applicationspecific warning parameters such as high limits for return gastemperature and discharge temperature.

[0023] Still referring to FIG. 1, module 12 may advantageously becommunicated with a system control box 40 such that commands issued byprocessor 14 can be enacted on the compressor, for example to changeoperating speed, turn off power, control crankcase heater operation, andthe like,

[0024] Module 12 in accordance with the present invention advantageouslyprovides for two forms of compressor protection, specifically, immediateand prognostic protection. Immediate protection is provided forcombinations of input indicating a failure is occurring or likely tooccur, and the compressor can be immediately shut down or other actiontaken. Prognostic protection is provided for combinations of sensorinput that indicate impending failure or degradation of compressorperformance, and suitable action may include adjusting the compressoroperation accordingly and issuance of a warning to the user and/ormaintenance personnel that compressor maintenance is required.

[0025] As set forth above, it is particularly advantageous in accordancewith the present invention to program module 12 and processor 14 todetect certain types of conditions based upon input from the differentcompressor sensors. It is preferred that the input sensors include inputas to compressor suction pressure, compressor suction temperature,compressor discharge pressure, compressor discharge temperature and oilpressure. It is important to note that the entering (suction pressureand temperature) and leaving (discharge pressure and temperature)refrigerant conditions are measured for each individual compressor. Withthese factors, flooded starts, liquid slugging and liquid floodback canbe detected, and appropriate action taken. With additional sensor inputas to the liquid injection set point, module 12 and processor 14 can beadapted to detect inadequate control of liquid injection as well, andtake appropriate action.

[0026] Thus, module 12 in accordance with the invention advantageouslyallows protection of the compressor using local sensors, preferablypositioned within about one foot of the compressor, which gatherinformation for processing by module 12 to take action dictated byprogramming in module 12 and also to allow communication from remotelocations, for example a monitoring station at a completely differentbuilding, site or location, as desired, so as to provide effectiveprotection of the compressor and, when applicable, products preserved byoperation of the compressor.

[0027] Flooded Start Detection

[0028] Liquid refrigerant will often return to a compressor during anoff cycle. Starting the compressor when it is filled with liquidrefrigerant can cause severe damage to the compressor includingcompressor failure. In accordance with the present invention, processor14 is advantageously adapted to detect a flooded start, as well as theseverity of the flooded start, and to either warn the user or shut downthe compressor, as appropriate.

[0029] By examining the suction temperature, suction pressure, dischargepressure, discharge temperature and oil pressure variations during thestartup of the compressor, processor 14 can differentiate a floodedstart as compared to a normal compressor start, as well as the severityof same, and take an appropriate control action.

[0030] Liquid Slugging

[0031] Liquid slugging is a major cause of compressor failure. Arefrigerant compressor is designed to compress vapor refrigerant andpump the refrigerant through the refrigeration/air conditioning system.Any liquid (i.e. non-compressible fluid), which is returned to thecompressor, even in small quantities, will stress the compressor andcan, in larger quantities, result in compressor damage. By examining thesuction temperature, suction pressure, discharge pressure, dischargetemperature and oil pressure variations during a period of liquidslugging, processor 14 can detect such slugging and, depending upon theseverity of same, take a control action including sending a warning to auser or maintenance personnel, or shut down the compressor, or both.

[0032] Liquid Injection Control

[0033] Inadequate control of liquid injection can result in inefficientcompressor operation and possible compressor failure. Certain highcompression ratio operating conditions require liquid refrigerant to beinjected in the compressor suction stream in order to maintain thecompressor discharge temperature within acceptable operating limits. Inaccordance with the present invention, the amount of liquid injection isoptimized based on energy efficiency and temperature reliabilityrequirements, and operation of the liquid injection valve is confirmedby comparing reduction in discharge temperature to an expected reductionin discharge temperature. Providing good liquid control optimizescompressor energy efficiency and reliability.

[0034] In accordance with the present invention, the opening of theliquid injection valve (output on module 12 ) is controlled based on theliquid injection set point and the measured compressor dischargetemperature. If the discharge temperature rises above the set point, thevalve opens until the discharge temperature drops below the set point.By evaluating the response of the valve (i.e., the measured reduction indischarge temperature) the module can determine if the valve is workingproperly by comparing the actual reduction in discharge temperature tothe expected reduction in discharge temperature.

[0035] Liquid Floodback

[0036] Liquid floodback is a major cause of compressor failure. Liquidrefrigerant returned to the compressor is one of the leading causes ofcompressor failure, and module 12 in accordance with the presentinvention is advantageously adapted to determine if, and to what extent,liquid refrigerant is entering the compressor.

[0037] Processor 14 advantageously is adapted to calculate or determinesuction superheat to determine if liquid refrigerant is entering thecompressor. If excessive liquid refrigerant is returned to thecompressor, it will extract heat from the refrigerant stream when itboils off thus resulting in lower operating temperatures. An expectedcompressor discharge temperature is calculated and compared to themeasured actual discharge temperature to determine the extent of thefloodback.

[0038] The module is programmed with refrigerant properties such that itcan calculate characteristics of the refrigerant type in use. With thisinformation, processor 14 calculates a saturation temperature based uponrefrigerant property tables and suction pressure. The suction superheatis then determined by subtracting the saturation temperature from thesuction temperature. If the suction superheat is below a warningthreshold, the user is warned of a floodback condition.

[0039] The expected discharge temperature is calculated as a function ofpressure ratio, suction temperature, compression coefficient andcompressor type. This is based upon the discovery that evaporation ofliquid refrigerant returned to the compressor will suppress thedischarge temperature. The difference between the expected dischargetemperature and actual discharge temperature is proportional to theamount of liquid refrigerant returned to the compressor.

[0040] Although the foregoing lists four particularly preferablyconditions which module 12 in accordance with the present invention isadapted to detect, a further listing of conditions corresponding todifferent sensor input and appropriate control actions corresponding tosame is provided in Table 1 below. TABLE 1 Failure Mode Possible ControlSensor(s) or Symptom Description Action(s) Required High High dischargepressure at Turn off the compressor Discharge Pressure Pressure thedischarge side of the if the discharge Protection compressor. pressureexceeds a threshold value. Compressor Compressor Overheating is a Turnoff the compressor Discharge Temperature Overheating major cause ofcompressor if the discharge failures. It has the temperature exceeds afollowing potential causes: threshold value. - broken discharge valveUnload Compressor. - low refrigerant charge - liquid injection failure -cylinder head cooling fan failure Low Oil Low oil pressure is also aTurn the compressor off Oil Pressure Pressure major cause of compressorif inadequate net oil Suction Pressure failures as it results in apressure is developed. * net oil pressure lack of lubrication. Itcalculated as oil has the following potential pressure - suction causes:pressure - liquid refrigerant in crankcase - high compressor wear - badoil pump. High Return High suction gas Warn user of high Suction gas Gastemperatures returned to suction temperatures. temperature Temperaturethe compressor can result in inadequate motor cooling and compressoroverheating. High High compressor cycling is Limit compressor Run/StopSignal Compressor generally an indication of cycling by including aCycles a bad system design or minimum off time. refrigerant control Warnuser of high problems. High compressor compressor cycles. cycles canlead to premature compressor failures. Low Low refrigerant charge canTurn compressor off Suction Pressure Refrigerant result in high motorand during low suction Discharge Temperature Charge dischargetemperatures and pressures or high freeze up of the dischargetemperatures. evaporator. Motor The motor can overheat due Turn thecompressor off Discharge Temperature Overheating to inadequaterefrigerant at high discharge cooling or running the temperatures.compressor above its design limits. Liquid Liquid refrigerant returnedWarn user when Suction Temperature Refrigerant to the compressor in thesuction/discharge Suction Pressure Floodback suction gas stream.superheat is low. Discharge Pressure Generally caused by Shut downcompressor Discharge Temperature excessive refrigerant feed withexcessive through the expansion floodback valve. Liquid Relatively largeamounts of Turn on warning light Suction Temperature Slugging liquid(refrigerant and/or or alarm. Suction Pressure oil) returned to theRecord fault in memory. Discharge Pressure compressor in a short Shutdown compressor if Discharge Temperature period of time. excessiveFlooded When a large volume of Turn on crankcase Suction TemperatureStart refrigerant accumulates in heater. Suction Pressure the crankcaseor oil sump Warn user of alarm. Discharge Pressure at shut down itdilutes Turn compressor off if Discharge Temperature oil. This can inturn lead excessive to a lack of compressor lubrication.

[0041] As can be seen, a substantial list of potential failure modes orsymptoms,and corresponding control actions are available and can beincorporated into the programming of module 12 in accordance with thepresent invention. In some instances, failures can be determined usingdifferent sensors. For example, as shown in Table 1, refrigerantfloodback can be determined from input obtained from four differentsensor combinations.

[0042] It is anticipated that the module in accordance with the presentinvention can advantageously be used to reduce failure rate of a largenumber of compressor parts, including for example main bearings,crankshaft, head gasket, discharge valve, suction valve, motor andconnecting rods, and the like.

[0043] In order to perform the desired operations in accordance with thepresent invention, module 12 and processor 14 are advantageouslyprovided with control functions utilizing triac outputs, specifically,triac outputs for CR1, CR2, liquid injection, crankcase heater on/off,alarm, unloader 1 and unloader 2.

[0044] Module 12 may advantageously be provided having non-volatilememory which can be accessed from remote locations as identified above,and is advantageously adapted to save operational data so as to assistin diagnosing problems. For example, it is anticipated that 8 K ofnon-volatile memory would be suitable for such purpose, althoughdifferent amounts of memory may be desired.

[0045] Fault conditions are also preferably saved in such memory forlater retrieval.

[0046] Human interface 38 in accordance with the present invention mayadvantageously consist of any known devices for communicatinginformation to the user, such as LED digits, LED's and buttons. Such aninterface allows a user to monitor compressor operational status, tomonitor compressor output status, to monitor compressor input values,and to setup configuration values. Human interface 38 may advantageouslybe directly driven by module 12, and processor 14 of same, and may haveany combination of display elements suitable for conveying the desiredinformation, for example, three 8-segment LED's, three push buttons, andeighteen individual LED's could be provided for conveying suchinformation.

[0047] Human interface 38 may further include a display listing variousfaults, for example, over current, high pressure, low pressure, oilpressure, floodback, motor temperature and crankcase heater malfunction.Such listings can be adapted to display one or more items as desired,for example, with LED's next to each item on the list, or in othermanners well known to a person of ordinary skill in the art, and arecommunicated with processor 14 such that control actions selected byprocessor 14 can include commands for operating interface 38 so as toprovide appropriate displays as well.

[0048] In accordance with the foregoing, it should readily beappreciated that a module has been provided which can be used withcompressors of varying types, for example screw compressors,reciprocating compressors, scroll compressors, rotary compressors andothers, so as to detect impending failure and take appropriate action.The module is particularly advantageous as compared to conventionalsystems in that actions are taken based upon combinations of input fromdifferent portions of the compressor, and remote actions are enabled.This advantageously allows for both prognostic and immediate protectionof the compressor.

[0049] It is to be understood that the invention is not limited to theillustrations described and shown herein, which are deemed to be merelyillustrative of the best modes of carrying out the invention, and whichare susceptible of modification of form, size, arrangement of parts anddetails of operation. The invention rather is intended to encompass allsuch modifications which are within its spirit and scope as defined bythe claims.

What is claimed:
 1. An apparatus for monitoring a compressor,comprising: a plurality of sensor inputs for receiving input regardingoperating parameters of a compressor; at least one control action outputfor sending a control action to said compressor; and a control membercommunicated with said plurality of sensor inputs and said controlaction output, said control member being adapted to analyze input fromsaid plurality of sensor inputs, to determine a control action basedupon said input and to send said control action to said at least onecontrol action output.
 2. The apparatus of claim 1, wherein said controlmember is adapted to receive input comprising compressor dischargepressure, compressor discharge temperature, compressor suction pressure,compressor suction temperature, oil pressure and a compressor on/offinput signal.
 3. The apparatus of claim 2, wherein said control memberincludes a memory storing a plurality of potential control actions, aplurality of adjustable operating parameters and a plurality of sensorinput value combinations corresponding to said plurality of potentialcontrol actions, and a processor adapted to compare said input to saidsensor input value combinations and select said control action from saidplurality of control actions.
 4. The apparatus of claim 3, wherein saidplurality of potential control actions includes a compressor shut downcommand, operation parameter adjusting commands and commands forindicating that maintenance is needed.
 5. The apparatus of claim 4,wherein said control member is further adapted to store informationregarding at least one of sensor input values, said control action andmaintenance alarms in said memory.
 6. The apparatus of claim 3, furthercomprising a communication member associated with said control memberand adapted to allow communication between said control member and aremote location.
 7. The apparatus of claim 6, wherein said plurality ofcontrol actions includes a command to issue a signal through saidcommunication member.
 8. The apparatus of claim 1, further comprising adisplay member communicated with said control member, said controlmember being adapted to display a message on said display membercorresponding to at least one of said input and said control action, andan indication of at least one compressor shut down or maintenancealarms; and to allow adjustment of at least one of said adjustableoperating parameters.
 9. The apparatus of claim 1, wherein said controlmember is adapted to identify a flooded start condition from said input.10. The apparatus of claim 9, wherein said input includes suctiontemperature, suction pressure, discharge pressure, discharge temperatureand oil pressure data, and said control actions include issuing aflooded start warning, altering an operating parameter of saidcompressor, shutting down said compressor, and combinations thereof. 11.The apparatus of claim 1, wherein said control member is adapted toidentify a liquid slugging condition from said input.
 12. The apparatusof claim 11, wherein said input includes suction temperature, suctionpressure, discharge pressure, discharge temperature and oil pressuredata, and said control actions include issuing a liquid sluggingwarning, altering an operating parameter of said compressor, shuttingdown said compressor, and combinations thereof.
 13. The apparatus ofclaim 1, wherein said control member is adapted to compare dischargetemperature from said input to a discharge temperature set point and tocontrol a liquid injection valve on said compressor based upon resultsof the comparison.
 14. The apparatus of claim 13, wherein said controlmember is adapted to open said liquid injection valve when saiddischarge temperature is greater than said set point.
 15. The apparatusof claim 13, wherein said control member has a memory storing expectedreactions to control actions taken on said liquid injection valve, andwherein said control member is adapted to compare actual change in saiddischarge temperatures to said expected reactions so as to identify amalfunctioning liquid injection valve.
 16. The apparatus of claim 1,wherein said control member is adapted to identify a liquid floodbackcondition from said input.
 17. A method for monitoring a compressor,comprising the steps of: obtaining input regarding a plurality ofcompressor operating parameters; feeding said input to a control member;analyzing said input with said control member to determine a controlaction based upon said input; and carrying out said control action onsaid compressor.
 18. The method of claim 17, wherein said inputcomprises compressor discharge pressure, compressor dischargetemperature, compressor suction pressure, compressor suctiontemperature, oil pressure and a compressor on/off input signal.
 19. Themethod of claim 18, wherein said control member includes a memorystoring a plurality of potential control actions and a plurality ofsensor input value combinations corresponding to said plurality ofpotential control actions; and wherein said control member selects saidcontrol action from said plurality of potential control actions.
 20. Themethod of claim 19, wherein said plurality of potential control actionsinclude a compressor shut down command, operation parameter adjustingcommands and commands for indicating that maintenance is needed.
 21. Themethod of claim 19, further comprising the step of storing informationregarding at least one of said input and said control action in saidmemory.
 22. The method of claim 17, wherein said input is obtained fromsensors positioned within about 1 foot of said compressor.
 23. Themethod of claim 17, further comprising the steps of enablingcommunication of said control member with a remote location, and atleast one of (a) sending information related to said control action tosaid remote location and (b) allowing access to information regardingsaid control action from said remote location.
 24. In combination, acompressor and control module system, comprising: a compressor; and acontrol module comprising a plurality of sensor inputs for receivinginput from said compressor; at least one control action output forconveying control actions to said compressor; and a control membercommunicated with said plurality of sensor inputs and said controlaction output, said control member being adapted to analyze input fromsaid plurality of sensor inputs, to determine a control action basedupon said input and to send said control action to said at least onecontrol action output.
 25. The system of claim 24, wherein said controlmember has a memory storing expected reactions to control actions takenon said liquid injection valve, and wherein said control member isadapted to compare actual change in said discharge temperatures to saidexpected reactions so as to identify a malfunctioning liquid injectionvalve.
 26. The system of claim 24, further comprising a plurality ofsensors associated with said compressor and connected to said sensorinputs.
 27. The system of claim 24, wherein said plurality of sensorscomprises sensors for measuring compressor discharge pressure,compressor discharge temperature, compressor suction pressure,compressor suction temperature, oil pressure and compressor on/off inputsignal.
 28. The system of claim 24, wherein said control member includesa memory storing a plurality of potential control actions and aplurality of sensor input combinations corresponding to said pluralityof potential control actions.
 29. The system of claim 28, wherein saidplurality of potential control actions include a compressor shut downcommand, operation parameter adjusting commands and commands forindicating that maintenance is needed.
 30. The system of claim 28,wherein said control member is further adapted to store informationregarding at least one of said input and said control action in saidmemory.
 31. The system of claim 24 further comprising a communicationmember associated with said control member and adapted to allowcommunication between said control member and a remote location.
 32. Thesystem of claim 31, wherein said at least one control action includes acommand to issue a signal through said communication member.
 33. Thesystem of claim 24, further comprising a display member communicatedwith said control member, said control member being adapted to display amessage on said display member corresponding to said control action. 34.The system of claim 33, wherein said message includes a value of atleast one sensor input, status of at least one control output and anindication of at least one compressor shut down or maintenance alarm.